A non-guard subcarrier OFDM modulation method and system based on four-way split IFFT end frequency shift and application thereof

Abstract

The application relates to the technical field of wireless communication and optical communication, and discloses a non-protected sub-carrier OFDM modulation method based on four-way split IFFT end frequency shift, a system and application thereof.The method splits N-point global sub-carriers of a standard OFDM into four groups according to four quadrants, respectively performs narrowband IFFT to generate sub-band signals near zero frequency, independently performs multi-stage 2 times interpolation and half-band filter up-sampling on the four-way signals, does not perform spectrum shift throughout the whole process, applies a complex exponential rotation factor to each way at the end to accurately shift the frequency to a target quadrant after being up-sampled to the final sampling rate, and finally superimposes and reconstructs a complete OFDM waveform in the time domain.The application completely cancels the frequency domain protection sub-carrier, realizes 100% spectrum utilization, replaces an anti-aliasing filter from a high-order steep filter into a low-order half-band filter, greatly reduces hardware cost, and is completely compatible with an existing OFDM communication system.

Description

Technical Field

[0001] This invention relates to the fields of wireless and optical communication technologies, and in particular to an unprotected subcarrier OFDM modulation method, system, and application based on four-way split IFFT end frequency shift. Background Technology

[0002] Orthogonal Frequency Division Multiplexing (OFDM) technology, as a core physical layer technology of modern wireless communication systems, has been widely used in fourth-generation (4G LTE / LTE-A) and fifth-generation (5G NR) mobile communication systems, and has been identified as a key modulation scheme for sixth-generation (6G) candidate technologies. In the LTE standard, OFDM, in conjunction with the cyclic prefix (CP) mechanism, effectively combats multipath fading and supports flexible resource block allocation and MIMO transmission. 5G NR further expands the OFDM parameter set (Numerology), supporting flexible configuration of subcarrier spacing from 15kHz to 240kHz to adapt to diverse scenarios ranging from enhanced mobile broadband (eMBB) and ultra-reliable low-latency communication (URLLC) to massive machine-type communication (mMTC).

[0003] At the wireless communication infrastructure level, OFDM modulation and demodulation functions are typically implemented by FPGA or ASIC chips in the baseband processing unit (BBU) on the base station side, or in the communication processor of the user terminal (UE). A typical implementation process is as follows: the modulation symbols to be transmitted (such as QPSK, 16QAM, 64QAM, etc.) are mapped to frequency domain subcarriers, transformed into time domain signals by IFFT, and then digitally up-converted (DUC) and analog up-converted to the radio frequency carrier for transmission. In fiber optic communication and wired transmission systems, OFDM is also used to address dispersion and nonlinear effects. Especially in coherent optical communication systems, the CO-OFDM scheme has proven to effectively improve spectral efficiency and transmission capacity. Furthermore, OFDM is widely used in many civilian and industrial fields such as WiFi (IEEE 802.11a / g / n / ac / ax), digital audio broadcasting (DAB), digital video broadcasting (DVB), and power line communication (PLC). It can be said that OFDM has become the foundational modulation technology for global digital communication infrastructure. Its performance directly affects the efficiency of spectrum resource utilization, the power consumption and cost of communication equipment, and even the technological evolution path of the entire communication industry.

[0004] Although OFDM technology is highly mature and has been deployed on a large scale in commercial applications, its core modulation architecture—a full-band multi-carrier modulation scheme based on a single N-point global IFFT—still has the following shortcomings:

[0005] First, the inherent spectrum waste caused by frequency domain guard subcarriers; the subcarriers generated by the single-channel full-band IFFT in the standard OFDM system have a full-domain rectangular spectrum characteristic; when subsequent interpolation and up-conversion processing are performed, the out-of-band sidelobes of each subcarrier expand and attenuate to both sides in the form of a sinc function; during digital domain interpolation, the original signal spectrum will generate periodic mirror copies in the interpolated Nyquist band, and these mirror spectra partially overlap with the effective signal spectrum, forming aliasing interference that cannot be completely eliminated; to suppress this aliasing and adjacent channel interference, a considerable number of blank subcarriers must be reserved on both sides of the effective subcarriers as guard bands in engineering; taking the standard LTE 20MHz bandwidth configuration as an example, the total number of subcarriers in the system is 2048, of which only 1200 are effective subcarriers, and the guard subcarriers and DC subcarriers occupy as many as 848, with a spectrum utilization rate of only about 58.6%; even in 5G In the large bandwidth configuration of NR, considering the strict requirements of adjacent channel leakage ratio (ACLR) and out-of-band transmit template, it is still necessary to reserve about 5% to 15% of the bandwidth as a protection interval; this kind of institutional redundancy has become a key bottleneck restricting system capacity in today's increasingly scarce spectrum resources.

[0006] Second, the traditional DUC timing, which involves frequency shifting followed by interpolation filtering, results in high hardware overhead. In standard OFDM systems, digital upconversion follows the paradigm of "frequency shifting first, then interpolation filtering." The frequency domain subcarriers are mapped to the complete digital frequency circle... Afterwards, multiple interpolation stages are required to increase the sampling rate. During each interpolation stage, the image of the high-frequency subcarrier is deeply entangled with the effective signal, requiring subsequent filters to have extremely steep transition bands and extremely high stopband suppression capabilities. In engineering implementation, high-order FIR filters (often exceeding 64 or even 128 orders) or cascaded integrator comb (CIC) filters are often required in conjunction with compensation filters, which consume a large amount of FPGA DSP slice resources and ASIC multiplier area. Taking the DUC module of a typical 4G base station RRU as an example, anti-aliasing filtering related logic can account for 25% to 40% of the total baseband processing resource consumption. High hardware overhead directly translates into increased chip area, increased power consumption, and increased cost, which runs counter to the development direction of miniaturization and green energy saving in communication equipment.

[0007] Third, traditional architectures are difficult to adapt to fragmented spectrum and dynamic spectrum access scenarios. One of the important features of 6G communication is support for ultra-wideband and dynamic spectrum sharing, which requires the system to flexibly utilize scattered idle spectrum resources. However, the single IFFT global modulation paradigm of standard OFDM requires subcarriers to fill the entire system bandwidth. Even if a certain frequency band is idle, its corresponding IFFT input points are still set to zero and the amount of computation will not decrease (the number of IFFT points is fixed, and the butterfly operation corresponding to the idle subcarrier still needs to be performed), resulting in a waste of computing power. At the same time, when transmission is required on non-contiguous fragmented spectrum, standard OFDM cannot directly support it and can only rely on alternative solutions such as filter bank multicarrier (FBMC) or universal filter multicarrier (UFMC). However, these solutions are incompatible with the existing OFDM system and cannot achieve smooth evolution.

[0008] Fourth, waveform spurious emissions and reactive power consumption are prominent issues in sparse spectrum scenarios. When the OFDM system operates in a sparse subcarrier mapping scenario (such as when only a small number of subcarriers are activated in IoT services), a single full-band IFFT still generates a time-domain waveform covering the entire bandwidth. A large amount of energy is concentrated in the frequency band that does not carry information, becoming useless out-of-band spurious emissions, which not only reduces power efficiency but also brings an extra burden to the RF front-end filtering.

[0009] Therefore, those skilled in the art urgently need a technical solution to achieve "in-situ replacement" of standard OFDM modulation modules by redesigning the internal signal processing flow and architecture of the modulator without changing the number of subcarriers, subcarrier spacing, symbol period and frame structure of the existing OFDM system. Summary of the Invention

[0010] The core technical problem solved by this invention is: how to completely eliminate the institutional redundancy of the protection subcarrier at the modulation architecture level while maintaining full compatibility with the existing OFDM system, achieve 100% spectrum utilization, and significantly reduce the hardware overhead of interpolation filtering.

[0011] Solving the aforementioned core technical problems is of great significance to those skilled in the art for the following reasons:

[0012] Spectrum resources are a non-renewable strategic resource for wireless communication. With the introduction of concepts such as full-spectrum access (0.1GHz–10THz) and integrated communication, sensing, and computing technologies in the 6G vision, the contradiction between spectrum supply and demand will be further exacerbated. According to ITU-R forecasts, by 2030, the cumulative global mobile communication spectrum demand will exceed 15GHz, while the available new spectrum resources are extremely limited. Any technological innovation that can improve the utilization rate of existing spectrum by 10%–20% is equivalent to releasing tens or even hundreds of MHz of new spectrum globally, with immeasurable economic and social benefits.

[0013] Meanwhile, energy consumption of communication equipment has become a core challenge for the industry's sustainable development. 5G base stations consume approximately 2 to 3 times more power than 4G base stations, with digital signal processing in the baseband processing unit accounting for a significant portion. If the filter design of the DUC module can be fundamentally simplified, replacing high-order anti-aliasing filters with low-order half-band filters, the power consumption per station can be reduced by tens of watts. Considering the millions of base stations worldwide, the energy-saving effect is extremely considerable.

[0014] The main reason why those skilled in the art need to overcome the aforementioned core technical problems is that the traditional "single IFFT global modulation + guard subcarrier anti-aliasing" framework has proven to have significant bottlenecks. Any incremental optimization within the existing framework—whether optimizing the subcarrier mapping algorithm, improving filter design, or adjusting the interpolation rate—cannot simultaneously break the constraints of both spectral efficiency and hardware complexity. Only by fundamentally reconstructing the timing relationship between IFFT modulation and spectrum shifting, shifting from "filling the spectrum first and then filtering" to "narrowband filtering first and then splicing," can a true systemic breakthrough be achieved.

[0015] To address the aforementioned core technical issues, this invention presents an unprotected subcarrier OFDM modulation method, system, and application based on four-way split IFFT end frequency shift. The aim is to uniformly split the N-point global subcarrier of standard OFDM into four independent subbands, each modulated by a narrowband IFFT. Then, in the time domain, a three-step operation of "2x interpolation + half-band filtering + rotation mixing" is performed sequentially. After all branches are upsampled to the system's final output sampling rate, a precise complex exponential rotation factor is applied at the end to complete spectrum splicing. Finally, a complete OFDM waveform is reconstructed through time-domain superposition. This architecture fundamentally overturns the inherent timing of the traditional DUC's "shift first, then filter" approach, enabling the image spectrum to be fully suppressed within the stopband of the low-cost half-band filter during each interpolation stage, thereby completely eliminating the dependence on frequency domain guard subcarriers. The entire technical solution is mainly applied to the baseband transmission processing of the downlink on the base station side and the uplink on the terminal side, and can also be extended to the electrical domain modulation front end of optical communication systems, enabling the system to generate aliasing-free, low-spurious OFDM waveforms even when all guard subcarriers are removed.

[0016] To achieve the above objectives, the specific technical solution of the present invention is a method for unprotected subcarrier OFDM modulation based on four-way split IFFT end frequency shift, the method comprising the following steps:

[0017] Step S1: Divide all effective subcarriers of the OFDM system into a first subcarrier subset, a second subcarrier subset, a third subcarrier subset, and a fourth subcarrier subset according to the four quadrants of the digital frequency circle;

[0018] Wherein, the first subcarrier subset corresponds to the frequency range ( , The second subcarrier subset corresponds to the frequency range ( The third subcarrier subset corresponds to the frequency range ( The fourth subcarrier subset corresponds to the frequency range ( , ), This refers to the system baseband sampling rate;

[0019] Narrowband IFFT modulation is performed on the first, second, third, and fourth subcarrier subsets respectively to generate four narrowband OFDM subband signals near the zero frequency. The effective bandwidth of each subband signal is constrained by ( , Within the range;

[0020] Step S2: Perform multi-level upsampling processing independently on the four narrowband OFDM subband signals. Each upsampling process includes:

[0021] A 2x interpolation operation is performed on the subband signal at the current sampling rate, and then the interpolated signal is filtered by a half-band filter to remove the mirror spectrum. The entire process of the multi-level upsampling process does not involve spectrum shifting.

[0022] Step S3: After all four narrowband OFDM sub-band signals have reached the final output sampling rate of the system, apply a time-domain complex exponential rotation factor to each narrowband OFDM sub-band signal to perform spectrum shifting, and shift each narrowband OFDM sub-band signal from the vicinity of zero frequency to its corresponding target quadrant frequency position.

[0023] S4. The four narrowband OFDM subband signals that have completed spectrum shifting are superimposed in the time domain to reconstruct a complete OFDM time-domain waveform without guarded subcarriers.

[0024] Preferably, the narrowband IFFT modulation in step S1 is implemented as follows: an N / 2-point IFFT transform is used, where only N / 4 frequency points located in the middle of the transform domain carry effective signals, and the remaining frequency points are set to zero, so that each sub-band signal forms a bandwidth of ( ) near the zero frequency. , Narrowband signal.

[0025] Preferably, the half-band filter in step S2 is selected from any one or more combinations of a 7th-order half-band filter, a 15th-order half-band filter, a 23rd-order half-band filter, and a 31st-order half-band filter.

[0026] Preferably, the 7th-order half-band filter has a passband ( The stopband rejection of the 15th-order half-band filter is not less than -64dB within the passband ( ). The stopband rejection of the 23rd order half-band filter is not less than -72dB within the passband ( ). The stopband suppression within the passband is not less than -104dB; the 31st-order half-band filter has a stopband suppression of not less than -104dB within the passband ( The stopband suppression within the range is not less than -136dB.

[0027] Preferably, the expression for the time-domain complex exponential twitch factor in step S3 is: ,in The time-domain sample number is... The imaginary unit is used to achieve a positive frequency shift when the rotation factor is positive. Frequency reversal is achieved when the rotation factor is negative. .

[0028] Preferably, the multi-stage upsampling processing in step S2 includes a combination of two-stage rotation-frequency shift operations and two-stage pure upsampling operations, specifically:

[0029] The first execution of the "2x interpolation + half-band filtering + rotating mixer" operation adds the two branch signals together, occupying the corresponding frequency range. The sampling rate is from Upgraded to ;

[0030] The second operation, "2x interpolation + half-band filtering + rotating mixer," sums the four branch signals to occupy the corresponding frequency range. The sampling rate is from Upgraded to ;

[0031] Subsequently, two "2x interpolation + half-band filtering" operations are performed without frequency shifting, reducing the sampling rate from... Upgraded to .

[0032] Preferably, in the "2x interpolation + half-band filtering + rotating mixer" operation, the signal spectrum after 2x interpolation is compressed to ( The image frequency signal group is located at ( The interval between the signal frequency group and the image frequency group is greater than 100°C. .

[0033] Preferably, the frequency mapping relationship of the four subcarrier subsets satisfies the following conditions:

[0034] After the first rotational mixing or Then, the first signal comes from ( , Mapped to ( The second signal comes from ( Mapped to ( The third signal comes from ( Mapped to ( The fourth signal comes from ( , Mapped to ( );

[0035] After a second rotational mixing process or Then, the first signal is finally mapped to ( The second signal is ultimately mapped to ( The third signal is ultimately mapped to ( The fourth signal is ultimately mapped to ( ).

[0036] Preferably, the method does not set any frequency domain protection subcarriers, and all N subcarriers are effective data subcarriers, achieving 100% spectrum utilization.

[0037] Preferably, the number of subcarriers N and the subcarrier spacing in the method are... Symbol period The frame structure is completely consistent with the standard OFDM system, and the receiver uses the standard FFT demodulation method to receive the data.

[0038] Preferably, each of the four narrowband OFDM sub-band signals can be independently turned on or off. When the frequency band corresponding to a narrowband OFDM sub-band signal is idle or unavailable, the modulation branch of that narrowband OFDM sub-band signal is turned off to save computational power consumption.

[0039] Preferably, the method is applicable to baseband transmission processing of base station downlink and terminal uplink in 4G LTE, 5G NR and 6G mobile communication systems.

[0040] Preferably, the method is also applicable to the electrical domain OFDM modulation front end in a coherent optical communication system, whereby the generated OFDM time-domain waveform is output to the optical modulator via a digital-to-analog converter.

[0041] Preferably, the spectrum shifting operation in step S3 is implemented based on the following mathematical model:

[0042] For the The path carries a signal ,in The time-domain sample number represents the frequency-shifted signal. ) is represented as:

[0043]

[0044] in, The sampling period is For the first The target relocation frequency of the route band, the target relocation frequency In the first cascaded rotational frequency shift, the value is taken as... In the second cascaded rotational frequency shift, the value is taken as The four sub-band signals are losslessly diffused from near zero frequency to the full frequency band through two cascaded rotational frequency shifts. );

[0045] The frequency shift mathematical model is characterized in that the rotation factor in the frequency shift operation is... Integer powers, in fixed-point implementations, are equivalent to performing operations on complex sample points. The precise multiplication operation does not introduce nonlinear distortion and phase noise. The term "lossless" means that the amplitude spectrum shape of the signal remains unchanged before and after the frequency shift, and the signal-to-noise ratio does not decrease due to the frequency shift operation.

[0046] Preferably, the cascaded rotational frequency shift in the frequency shift mathematical model is implemented using the following recursive relationship:

[0047] After the first-stage frequency shift, the signal frequency range is from ( ) Expand to ( , The sampling rate is from Upgraded to ;

[0048] After the second-stage frequency shift, the signal frequency range is from ( ) Expand to ( , The sampling rate is from Upgraded to 2 ;

[0049] The recursive relationship can be generalized to more series using mathematical induction. Each cascade doubles the spectral range, and after K cascades, the spectral range increases from the initial (…). Expand to ( ).

[0050] Preferably, the present invention also discloses an unprotected subcarrier OFDM modulation system based on four-way split IFFT end frequency shift, the system being used to implement the method, comprising:

[0051] The subcarrier splitting and narrowband IFFT modulation module is configured to evenly split all effective subcarriers of the OFDM system into four subcarrier subsets according to the four quadrants of the digital frequency circle, and independently perform narrowband IFFT modulation on each subcarrier subset to generate four narrowband OFDM subband signals near the zero frequency.

[0052] The multi-level interpolation and half-band filtering upsampling module is connected to the subcarrier splitting and narrowband IFFT modulation module and is configured to independently perform multi-level "2x interpolation + half-band filtering" upsampling processing on the four narrowband OFDM subband signals, without performing spectrum shifting throughout the process.

[0053] The end complex exponential frequency shifting module is connected to the multi-level interpolation and half-band filtering upsampling module. It is configured to apply a complex exponential rotation factor to each narrowband OFDM sub-band signal to shift it to its respective target quadrant frequency position after the four narrowband OFDM sub-band signals reach the final output sampling rate of the system.

[0054] The time-domain superposition and reconstruction module is connected to the end complex exponential frequency shifting module and is configured to superimpose the four frequency-shifted narrowband OFDM subband signals in the time domain to generate a complete OFDM time-domain waveform without guarded subcarriers.

[0055] Preferably, the subcarrier splitting and narrowband IFFT modulation module is provided with an N / 2-point IFFT operation unit, wherein only N / 4 of the input frequency points of the N / 2-point IFFT operation unit are activated to carry the effective signal.

[0056] Preferably, the multi-level interpolation and half-band filtering upsampling module includes multiple upsampling stages connected in series, wherein each upsampling stage includes:

[0057] The 2x interpolation submodule is configured to insert a zero-value sample between every two adjacent samples of the input signal;

[0058] A half-band filtering submodule, connected to the 2x interpolation submodule, is configured to filter the interpolated signal to remove the mirror spectrum generated by interpolation. The filtering coefficients of the half-band filtering submodule are generated based on the equiripple design method.

[0059] Preferably, the first two upsampling stages of the multi-stage interpolation and half-band filtering upsampling module are further provided with a rotating frequency shifting submodule, which is configured to combine the filtered signal with... or Multiplying complex exponential sequences, where The time-domain sample number, It is the imaginary unit.

[0060] Preferably, the complex exponential rotation factor used in the frequency shift operation of the terminal complex exponential frequency shift module is . With its cascaded forms, frequency shifting operation does not introduce additional phase noise and amplitude distortion.

[0061] Preferably, the effective subcarriers in the output waveform of the system continuously fill the entire system frequency band. It does not contain any blank guard subcarriers on both sides.

[0062] Preferably, the system is implemented in the form of an FPGA or ASIC chip, and the multiplier resource consumption of the half-band filter submodule is reduced by more than 50% compared with the anti-aliasing filter in the standard OFDM modulator.

[0063] Preferably, the present invention also discloses a wireless communication transmitting device, which includes:

[0064] The baseband signal processing unit is configured to generate a sequence of modulation symbols to be transmitted;

[0065] The system, connected to the baseband signal processing unit, is configured to modulate the modulation symbol sequence into an OFDM time-domain waveform with unguarded subcarriers;

[0066] A digital-to-analog converter, connected to the OFDM modulator, is configured to convert the OFDM time-domain waveform into an analog baseband signal;

[0067] An RF upconversion module, connected to the digital-to-analog converter, is configured to upconvert the analog baseband signal to the RF carrier frequency;

[0068] A power amplifier, connected to the radio frequency upconversion module, is configured to amplify the power of the radio frequency signal;

[0069] An antenna, connected to the power amplifier, is configured to radiate radio frequency signals into free space.

[0070] Preferably, the wireless communication transmitting device is any one of a 4G LTE base station, a 5G NR base station, a 6G base station, a user terminal device, a WiFi access point, or a mobile communication relay node.

[0071] Preferably, the present invention also discloses a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, is capable of implementing the steps of the method.

[0072] Compared with the prior art, the technical solution disclosed in this application has the following non-obvious technical features:

[0073] Compared with existing standard OFDM modulation technology, the present invention has the following non-obvious technical features:

[0074] Technical Feature 1: This invention adopts a parallel modulation architecture with four-quadrant splitting. In the prior art, OFDM modulation uses a single N-point global IFFT to fill all subcarriers in the entire domain at once, which is a long-established technical paradigm in the field. This application breaks through by uniformly splitting the N-point global subcarriers into four independent subsets corresponding to the four quadrants of the digital frequency circle, and using N / 2-point IFFT for each subset but only activating the middle N / 4 frequency points. This architecture design of "replacing large IFFT with small IFFT and full-coverage with local concentration" is not the conventional thinking of those skilled in the art when facing the problem of spectrum efficiency, because splitting the IFFT intuitively increases the number of processing branches, which is usually considered to increase rather than reduce complexity.

[0075] Technical Feature Two: This invention reverses the processing timing of interpolation filtering followed by spectrum shifting. The DUC module in a standard OFDM system strictly follows the timing sequence of "frequency domain shifting first, then interpolation filtering," a sequence that has been included in many classic communication principle textbooks and used in industry for nearly thirty years. This application creatively postpones all spectrum shifting operations to the high sampling rate output, maintaining the signal in a narrow band near zero frequency during the intermediate multi-stage interpolation filtering phase. This timing reversal fixes the interval between the mirror spectrum generated by each interpolation stage and the effective signal. Therefore, anti-aliasing can be achieved using low-order half-band filters; reversing a basic signal processing flow that has been maturely used for decades and combining it with split-path IFFT to produce a synergistic effect is by no means obvious to those skilled in the art.

[0076] Technical Feature 3: This invention implements an end-spectrum splicing strategy based on "lossless rotating mixer"; existing technologies typically use a digitally controlled oscillator (NCO) in conjunction with a mixer during spectrum shifting, introducing quantization phase noise and spurious signals; this application adopts... The complex exponential twitch factor is shifted stepwise, and the phase increment of this twitch factor is exactly... In numerical terms, it is equivalent to a precise rotation of a fixed point. (Approximate quantization) without introducing additional phase noise and amplitude distortion; especially after the two-stage rotation factor cascade, the spectral mapping relationship precisely transforms the four signals from The concentrated area diffuses without loss to The full bandwidth range, the mapping accuracy depends on a very simple rotation factor. This design idea of ​​"achieving complex spectrum shifting with simple mathematical symmetry" has outstanding non-obviousness.

[0077] Technical Feature 4: This invention achieves a complete solution for completely eliminating the protection subcarrier. Although there has long been a technical vision in the field of "hoping to eliminate the protection subcarrier," all attempts to date have remained at the level of patching methods such as frequency domain windowing and time domain pulse shaping, which cannot simultaneously meet the EVM and spectrum template specifications. This application achieves the complete elimination of the protection subcarrier without reducing any radio frequency specifications through the synergistic effect of three stages: "splitting IFFT → multi-level interpolation filtering → end frequency shifting splicing." This technical effect is not a simple superposition of the effects of the above steps, but a qualitative change caused by the synergistic cooperation between the steps.

[0078] Compared with the prior art, the present invention has the following beneficial effects:

[0079] Compared with existing standard OFDM modulation technology, the technical solution of the present invention has the following advantages:

[0080] 1. This invention improves spectrum utilization to 100%. Because this application eliminates the risk of image aliasing during the interpolation process by interpolating and filtering four narrowband sub-band signals separately and then frequency-shifting and splicing them at the end, no blank guard subcarriers are needed on both sides of the effective frequency band of the OFDM system. All subcarriers can be used for data transmission, and the spectrum utilization is improved from about 58.6% of the existing LTE system and about 85% to 92% of the 5G system to 100%. Taking a 100MHz system bandwidth as an example, it is equivalent to increasing the effective data transmission bandwidth by 8 to 15MHz, which significantly improves the system capacity without adding spectrum resources.

[0081] 2. This invention significantly reduces the hardware overhead of the anti-aliasing filter; in the prior art, to suppress the image aliasing generated after high-frequency subcarrier interpolation, high-order steep filters are required, often with an order of 64 or higher; in this application, because the narrowband signal spectrum is highly concentrated near zero frequency, the guard interval between the interpolated image and the effective signal is fixed to be greater than [missing information]. By using 7th, 15th, 23rd or 31st order half-band filters, stopband rejection better than -64dB to -136dB can be achieved; the filter order is reduced by more than 50%, and the number of multipliers and DSP resource consumption are reduced by 50% to 70%, while chip area and dynamic power consumption are reduced simultaneously.

[0082] 3. The purity of the waveform output by this invention is superior to existing standards; the timing of filtering before frequency shifting in this application ensures that all interpolated images are completely filtered out before frequency shifting, and the frequency shifting operation only applies to the pure baseband signal without generating new images or out-of-band spurious signals; the key indicators of the output waveform, such as out-of-band rejection ratio, error vector magnitude (EVM), and adjacent channel leakage ratio (ACLR), are theoretically superior to the standard OFDM scheme.

[0083] 4. This invention is fully compatible with existing OFDM communication systems; the modification in this application is to the modulation implementation architecture at the transmitting end, specifically the number of subcarriers N and the subcarrier spacing. Symbol period The cyclic prefix length and frame structure are consistent with the standard OFDM; the receiver does not need to make any changes and can still use standard FFT demodulation, so it can be seamlessly connected to 4G LTE, 5G NR and future 6G communication systems, achieving a smooth upgrade.

[0084] 5. This invention supports sparse spectrum and fragmented spectrum access; four independent sub-band modulation branches can be turned on or off independently as needed; when the system is working in a narrowband IoT scenario or needs to utilize fragmented spectrum, only the corresponding sub-band branch needs to be activated, and the blank frequency band does not participate in the calculation at all, avoiding the reactive power consumption of standard OFDM global IFFT, while having the flexibility to directly adapt to non-continuous spectrum allocation. Attached Figure Description

[0085] Figure 1 This is a flowchart of the method described in this invention;

[0086] Figure 2 This is a schematic diagram of the method described in this invention;

[0087] Figure 3 This is a graph showing the amplitude-frequency and phase-frequency characteristics of the output of the 7-tap equal-ripple HBF filter described in this invention, wherein the passband ( ), stopband ( Stopband rejection -64.6dB;

[0088] Figure 4 This is a graph showing the amplitude-frequency and phase-frequency characteristics of the output of the 7-tap equal-ripple HBF filter described in this invention, wherein the passband ( ), stopband ( Stopband rejection -39dB;

[0089] Figure 5 This is a graph showing the amplitude-frequency and phase-frequency characteristics of the output of the 15-tap equiripple HBF filter described in this invention, wherein the passband ( ), stopband ( Stopband rejection -72.4dB;

[0090] Figure 6 This is a graph showing the amplitude-frequency and phase-frequency characteristics of the output of the 23-tap equal-ripple HBF filter described in this invention, wherein the passband ( ), stopband ( Stopband rejection -104.7dB;

[0091] Figure 7This is a graph showing the amplitude-frequency and phase-frequency characteristics of the output of the 31-tap equiripple HBF filter described in this invention, wherein the passband ( ), stopband ( Stopband rejection -136.5dB;

[0092] Figure 8 This is a schematic diagram of the digital channel processing principle of the existing 5G / 6G OFDM system described in this invention;

[0093] Figure 9 This is a schematic diagram of the system described in this invention;

[0094] Figure 10 This is a schematic diagram of the structure of the device described in this invention. Detailed Implementation

[0095] The following is in conjunction with the appendix Figures 1 to 10 The main technical features of the present invention are described in detail below:

[0096] In the technical solution of this invention, the subcarrier grouping strategy of four-quadrant splitting is to group the N-point global subcarriers of standard OFDM according to the digital frequency circle. The four quadrants are evenly divided into four independent subcarrier subsets, corresponding to frequency intervals ( ), ( ), ( )and( Each subcarrier subset undergoes independent subsequent modulation processing. This strategy is the premise and foundation of all subsequent operations. By splitting the global subcarriers into four quadrants, each subcarrier group is naturally separated in the frequency domain, creating conditions for the subsequent "filter first, then frequency shift" timing reversal. Without this splitting, all subcarriers would be aliased across the entire frequency band, making lossless splicing after narrowband filtering impossible. This feature directly determines the feasibility of the scheme and the feasibility of canceling the protective subcarriers.

[0097] In the technical solution of this invention, the narrowband IFFT modulation and zero-frequency concentration strategy involves performing an N / 2-point IFFT transform on each subset of subcarriers, but only carrying effective signals at the middle N / 4 frequency points of the transform domain, while setting the remaining frequency points to zero, so that the energy of each output signal is concentrated near the zero frequency. Within an extremely narrow bandwidth, this strategy ensures that each signal remains in a narrow-band state throughout the subsequent interpolation and filtering stages, maintaining a sufficient frequency domain interval (greater than) between the effective signal and the image signal generated by interpolation. This feature enables low-order half-band filters to effectively filter out image reflections; this characteristic is the technical basis for reducing the hardware overhead of filters.

[0098] In the technical solution of this invention, the timing reversal of "interpolation and filtering first, followed by spectrum shifting" means that during the multi-level upsampling process, all interpolation and filtering operations are completed when the signal is in a zero-frequency narrowband state, without any spectrum shifting operation. The spectrum shifting is delayed until the end after all upsampling is completed and before the final output. This timing reversal fundamentally avoids the participation of high-frequency signals in the interpolation process, ensuring that the mirror spectrum never overlaps with the effective signal, thereby completely eliminating the institutional dependence on the guard subcarrier. This timing reversal is the key mechanism for solving the core problem.

[0099] In the technical solution of this invention, the precise frequency shifting of the terminal complex exponential rotation factor is achieved by applying a method to each pure narrowband signal at the final output sampling rate of the system. A complex exponential twitch factor, in the form of a two-stage cascaded frequency shifter, losslessly shifts four signals from near zero frequency to their respective target frequencies in the four quadrants; this precise frequency shifting achieves "lossless" splicing of the spectrum; the phase increment of the twitch factor is exactly... The numerical implementation is accurate, without introducing phase noise and amplitude distortion, ensuring that the EVM index of the reconstructed waveform after frequency shift is not degraded; this feature is the core operation to ensure the quality of the final output waveform.

[0100] In the technical solution of this invention, the reconstruction strategy of time-domain superposition is to directly add the four sub-band signals that have completed precise frequency shifting in the time domain, and reconstruct the complete broadband OFDM time-domain waveform using the superposition principle of linear systems; this strategy concisely and efficiently completes the final synthesis of the four signals from frequency domain dispersion to time domain aggregation; because each sub-band strictly complements and covers the other in the frequency domain (continuously covering the entire...) The time-domain superposition will not produce inter-carrier interference; this feature is directly related to the integrity and correctness of the output waveform.

[0101] In the technical solution of this invention, the general extended framework of N-way OFDM is to abstract the specific implementation of four-way splitting into a general architecture of M-way (M≥2) splitting. By repeatedly calling the three-step operation of "2x interpolation + half-band filtering + rotation mixing", any OFDM signal can be synthesized step by step after removing the image frequency group through the half-band filter. This framework reflects the universality and scalability of the technical solution of this application. Four-way splitting is a special case of M=4. This framework can adapt to different bandwidth requirements and fragmented spectrum scenarios. When it is necessary to utilize non-continuous spectrum, the corresponding branch can be opened as needed. This feature ensures the future compatibility and application breadth of the solution.

[0102] In the technical solution of this invention, the hierarchical design of the half-band filter family involves using half-band filters of different orders (including 7th, 15th, 23rd, and 31st orders) at different interpolation stages. The corresponding filter order is matched according to the stopband suppression requirements of that stage. The passband and stopband boundary design of each filter stage ensures that the image spectrum falls completely within the stopband range. This hierarchical design achieves refined optimization of hardware overhead. Low-order filters are used in stages with lower stopband suppression requirements, while high-order filters are used in stages with higher requirements, avoiding the waste of resources by uniformly using high-order filters throughout the system. This feature is an important support for the goal of reducing hardware burden.

[0103] The following is in conjunction with the appendix Figures 1 to 10 The embodiments of the present invention will be described in detail below:

[0104] refer to Figure 1 This document illustrates a flowchart of an unprotected subcarrier OFDM modulation method based on four-way split IFFT end-shift frequency according to one or more embodiments of this application. The method is applied to the baseband transmission processing unit of a wireless communication base station or user terminal, and is also applicable to the electrical domain OFDM modulation front-end of a coherent optical communication system. It includes the following steps: Step S1, subcarrier four-way quadrant splitting and narrowband IFFT group modulation; Step S2, multi-level interpolation and half-band filtering upsampling; Step S3, end-shift complex exponential frequency shift; Step S4, time-domain superposition and reconstruction. Figure 2 The overall principle architecture of this method is further illustrated, in which the four parallel branches are each cascaded through "2x interpolation + half-band filtering + rotating mixing" and then added together to finally achieve the complete OFDM waveform output without guarded subcarriers.

[0105] In one or more embodiments, step S1 configures the OFDM modulator's subcarrier splitting and narrowband IFFT modulation module to perform the following operation: splitting the N-point globally effective subcarriers of the standard OFDM system according to the digital frequency circle. The four quadrants are evenly divided into four independent subcarrier subsets. Specifically, the first subcarrier subset corresponds to the frequency range ( The second subcarrier subset corresponds to the frequency range ( The third subcarrier subset corresponds to the frequency range ( The fourth subcarrier subset corresponds to the frequency range ( ),in This represents the system baseband sampling rate.

[0106] In one or more embodiments, the subcarrier splitting and narrowband IFFT modulation module internally includes an N / 2-point IFFT operation unit. After the modulation symbol sequence to be transmitted (such as QPSK symbols, 16QAM symbols, or 64QAM symbols) is mapped to each subcarrier subset, the N / 2-point IFFT operation unit performs a narrowband IFFT transform on each of the four subcarrier subsets. It is worth noting that in each N / 2-point IFFT transform, only the N / 4 frequency points located in the middle of the transform domain carry valid signals, while the remaining frequency points are all set to zero. This operation ensures that the energy of each output signal is concentrated near the zero frequency (…). Within an extremely narrow bandwidth, four narrowband OFDM sub-band signals near zero frequency are formed. Because each sub-band signal has no high-frequency components throughout its entire range, its spectrum is highly convergent, and it naturally does not have the risk of out-of-band leakage.

[0107] In one or more embodiments, the multi-level interpolation and half-band filtering upsampling module in step S2 is configured to independently perform multi-level upsampling processing on the four narrowband OFDM subband signals generated in step S1.

[0108] Each level of upsampling processing includes:

[0109] First, the 2x interpolation submodule inserts a zero-value sample between every two adjacent samples of the subband signal at the current sampling rate, thereby doubling the sampling rate.

[0110] Then, the half-band filtering submodule performs low-pass filtering on the interpolated signal to filter out the mirror spectrum generated by the interpolation operation.

[0111] Specifically, when the signal bandwidth is ( After being interpolated by a factor of 2, the spectrum of a narrowband signal is compressed to ( ). ), while the image frequency signal group generated by interpolation is located in ( The frequency domain spacing between the signal frequency group and the image frequency group is greater than 100%. The filter coefficients of this half-band filtering submodule are generated based on an equiripple design method, and its passband and stopband boundary design ensures that the mirror spectrum falls completely within the filter's stopband range. Throughout this multi-stage upsampling process, the system does not perform any spectrum shifting operations. All interpolation and filtering are completed when the signal is in a zero-frequency narrowband state, thus completely avoiding the high-frequency interpolation aliasing problem in traditional OFDM, without the need for guard subcarriers to assist in anti-aliasing.

[0112] In one or more embodiments, the multi-stage upsampling process includes a combination of two-stage rotation frequency shift operations and two-stage pure upsampling operations.

[0113] The first execution of the "2x interpolation + half-band filtering + rotating mixer" operation adds the two branch signals together, occupying the corresponding frequency range. The sampling rate is from Upgraded to ;

[0114] The second operation, "2x interpolation + half-band filtering + rotating mixer," sums the four branch signals to occupy the corresponding frequency range. The sampling rate is from Upgraded to ;

[0115] Subsequently, two "2x interpolation + half-band filtering" operations are performed without frequency shifting, reducing the sampling rate from... Upgraded to When the required system output sampling rate differs, this number of stages can be adjusted accordingly based on actual needs.

[0116] In one or more embodiments, step S3 configures the end complex exponential frequency shifting module as follows: after all four narrowband OFDM subband signals have completed multi-level upsampling and reached the final output sampling rate of the system, a time-domain complex exponential rotation factor is applied to each subband signal to perform spectrum shifting, thereby shifting each narrowband subband signal from the interval near zero frequency to its corresponding target quadrant frequency position.

[0117] Specifically, the expression for this time-domain complex exponential twitch factor is: ,in The time-domain sample number, The imaginary unit. When the rotation factor is positive. Time to achieve forward frequency shift When the rotation factor is negative Frequency reverse shift is achieved in time. The phase increment of this rotation factor is exactly . In fixed-point implementation, this is equivalent to performing calculations on complex samples. The precise multiplication operation does not introduce additional phase noise or amplitude distortion. In this embodiment, the frequency shift operation is entirely postponed to the high sampling rate output. Since the interpolation image in the signal before frequency shifting has been completely filtered out in step S2, the frequency shift operation itself does not generate any new images or out-of-band leakage.

[0118] More specifically, the frequency mapping relationship of the four subcarrier subsets satisfies the following condition: after the first rotation mixing or Then, the first signal comes from ( Mapped to ( The second signal comes from ( Mapped to ( The third signal comes from ( Mapped to ( The fourth signal comes from ( Mapped to ( After a second rotational mixing process or Then, the first signal is finally mapped to ( The second signal is ultimately mapped to ( The third signal is ultimately mapped to ( The fourth signal is ultimately mapped to ( ).

[0119] In one or more embodiments, step S4 configures the time-domain superposition and reconstruction module to directly superimpose the four narrowband OFDM sub-band signals that have undergone precise frequency shifting in the time domain. Since the four sub-band signals have achieved strict complementary coverage in the frequency domain (continuously covering the entire...) The sub-bands are divided into intervals, and there is no spectral overlap between them. Utilizing the superposition principle of linear systems, the complete broadband OFDM time-domain waveform can be reconstructed after time-domain superposition. In this reconstructed waveform, the subcarriers continuously fill the effective bandwidth, eliminating the need for any blank guard subcarriers on both sides, thus completely eliminating the spectral redundancy of traditional OFDM.

[0120] In one or more embodiments, the half-band filter in step S2 may be selected from any one or more combinations of a 7th-order half-band filter, a 15th-order half-band filter, a 23rd-order half-band filter, and a 31st-order half-band filter.

[0121] Optionally or additionally, half-band filters of different orders can be used in different interpolation stages. Specifically, 7th or 15th order half-band filters are used in interpolation stages with lower stopband suppression requirements, while 23rd or 31st order half-band filters are used in interpolation stages with higher stopband suppression requirements, thereby achieving fine optimization of hardware overhead while ensuring filtering performance.

[0122] In one or more embodiments, the "2x interpolation + half-band filtering + rotation mixing" operation in step S2 can be replaced with a "2x interpolation + half-band filtering" operation without rotation frequency shifting, i.e., only pure upsampling is performed. This corresponds to scenarios where the system does not need to perform spectrum shifting. In some embodiments, when the frequency band corresponding to one of the four narrowband OFDM sub-band signals is idle or unavailable, that sub-band modulation branch can be independently shut down to save computational power consumption.

[0123] In one or more embodiments, the spectrum shifting operation in step S3 is implemented based on the following mathematical model: for the first The path carries a signal ,in The time-domain sample number represents the frequency-shifted signal. Represented as:

[0124]

[0125] in The sampling period is For the first The target relocation frequency of the route. In the first cascaded rotational frequency shift, the value is taken as ± In the second cascaded rotational frequency shift, the value is taken as Through two cascaded rotational frequency shifts, the four sub-band signals are shifted from near zero frequency ( Lossless diffusion from the interval to the full frequency band ( ).

[0126] This cascaded rotational frequency shift is achieved using the following recursive relationship: After the first stage of frequency shift, the signal frequency range changes from ( ) Expand to ( The sampling rate is from Upgraded to After the second-stage frequency shift, the signal frequency range changes from ( ) Expand to ( The sampling rate is from Upgraded to This recursive relationship can be generalized to more series through mathematical induction—each cascade doubles the spectral range, and after K cascades, the spectral range increases from the initial ( Expand to ( ).

[0127] In one or more embodiments, to ensure the atomicity of configuration of key parameters during digital signal processing, especially when the method runs on a multi-core processor or parallel processing architecture, the system performs parameter updates through a semaphore mechanism. Specifically, this includes: acquiring a configuration parameter update lock; reading the current filter coefficients or twiddle factor configuration; merging the parameter to be updated with the existing configuration; writing the final configuration to the corresponding register or memory mapping table; and releasing the semaphore.

[0128] In one or more embodiments, in response to the interpolation filter output power in a subband signal processing link exceeding a preset threshold (indicating possible image residue), the system executes an error handling procedure, wherein the error handling procedure includes at least one of the following operations: increasing the order of the halfband filter in the link to enhance stopband suppression, reducing the power of the input signal of the link to avoid nonlinear distortion, recording an error log and marking the subband link as an abnormal state.

[0129] In one or more embodiments, the method achieves unprotected subcarrier modulation of the OFDM system through the coordinated operation of steps S1 to S4, increasing the spectrum utilization to 100%. At the same time, it uses a low-order half-band filter to replace the traditional high-order anti-aliasing filter, which significantly reduces the hardware overhead and power consumption of baseband processing.

[0130] refer to Figure 9 This paper illustrates a schematic diagram of an unprotected subcarrier OFDM modulation system based on four-way split IFFT end-shift frequency according to one or more embodiments of this application. This system is applied to the baseband transmission processing link of a wireless communication base station or user terminal, and can also be embedded in the electrical domain modulation front-end of a coherent optical communication system. The system includes four core modules: a subcarrier splitting and narrowband IFFT modulation module, a multi-level interpolation and half-band filtering upsampling module, an end-complex exponential frequency shifting module, and a time-domain superposition and reconstruction module.

[0131] In one or more embodiments, the subcarrier splitting and narrowband IFFT modulation module is configured to uniformly split all effective subcarriers of the OFDM system into four subcarrier subsets according to the four quadrants of the digital frequency circle, and independently perform narrowband IFFT modulation on each subcarrier subset to generate four narrowband OFDM subband signals near the zero frequency. The subcarrier splitting and narrowband IFFT modulation module internally includes an N / 2-point IFFT operation unit. Only N / 4 of the input frequency points of this N / 2-point IFFT operation unit 211 are activated to carry effective signals, while the remaining frequency points are set to zero. Specifically, the subcarrier splitting and narrowband IFFT modulation module receives a modulation symbol sequence from the baseband signal processing unit, which is distributed to the IFFT input ports corresponding to the four quadrants according to the subcarrier index. The four N / 2-point IFFT operation units operate in parallel, outputting four narrowband time-domain signals near the zero frequency, with the effective bandwidth of each signal constrained by (…). Within the range.

[0132] In one or more embodiments, the multi-stage interpolation and half-band filtering upsampling module is connected to the subcarrier splitting and narrowband IFFT modulation module, configured to independently perform multi-stage "2x interpolation + half-band filtering" upsampling processing on the four narrowband OFDM subband signals, without any spectrum shifting. This module includes multiple cascaded upsampling stages. Each upsampling stage includes:

[0133] The 2x interpolation submodule is configured to insert a zero-value sample between every two adjacent samples of the input signal;

[0134] The half-band filtering submodule is connected to the 2x interpolation submodule and is configured to filter the interpolated signal to remove the mirror spectrum generated by the interpolation.

[0135] The filtering coefficients of the half-band filtering submodule are generated based on the equiripple design method, and its passband and stopband boundary design ensures that the image spectrum falls completely within the stopband range.

[0136] In one or more embodiments, each half-band filter submodule can be selected from any one of 7th, 15th, 23rd or 31st order half-band filters, and different upsampling stages can use half-band filters of different orders.

[0137] In one or more embodiments, the multi-stage interpolation and half-band filtering upsampling module performs a combination of two-stage rotation frequency shifting operations and two-stage pure upsampling operations. Figure 2 This processing architecture is illustrated: the first two upsampling stages each include a rotation frequency shift submodule 2213, configured to combine the filtered signal with... or Multiply the complex exponential sequences.

[0138] After the first execution of "2x interpolation + half-band filtering + rotating mixer", the sum of the two branch signals occupies the frequency spectrum range ( The sampling rate is from Upgraded to ;

[0139] After the second execution of "2x interpolation + half-band filtering + rotating mixer", the sum of the four branch signals occupies the frequency spectrum range ( The sampling rate is from Upgraded to .

[0140] The two subsequent cascaded upsampling stages only perform "2x interpolation + half-band filtering" without frequency shifting, reducing the sampling rate from... Upgraded to .

[0141] In one or more embodiments, the end-of-line complex exponential frequency shifting module is connected to the multi-stage interpolation and half-band filtering upsampling module, configured to apply a complex exponential rotation factor to each narrowband OFDM sub-band signal to shift it to its respective target quadrant frequency position after the four narrowband OFDM sub-band signals reach the system's final output sampling rate. This complex exponential rotation factor is... With its cascaded forms, frequency shifting operation does not introduce additional phase noise and amplitude distortion.

[0142] In one or more embodiments, the time-domain superposition and reconstruction module is connected to the end-of-line complex exponential frequency shift module, configured to superimpose four frequency-shifted narrowband OFDM subband signals in the time domain to generate a complete OFDM time-domain waveform with unguarded subcarriers. The output waveform of this module continuously fills the entire system frequency band with effective subcarriers. It does not contain any blank guard subcarriers on both sides.

[0143] In one or more embodiments, the N / 2-point IFFT operation unit in the subcarrier splitting and narrowband IFFT modulation module can be replaced with an N / 4-point IFFT operation unit in conjunction with frequency domain zero-placing operation to achieve a similar narrowband signal generation function. The purpose is to flexibly select the implementation architecture according to different hardware resources and performance requirements.

[0144] In one or more embodiments, the half-band filtering sub-module in the multi-level interpolation and half-band filtering upsampling module can all adopt a 31st-order equiripple half-band filter to achieve the highest stopband rejection (-136.5dB), thus making it suitable for application scenarios with extreme requirements for out-of-band emission suppression.

[0145] In one or more embodiments, the spectrum shifting operation in the terminal complex exponential frequency shifting module is specifically implemented according to the following mathematical model: for the i-th subband signal ( ), frequency-shifted signal for:

[0146] .

[0147] Among them, the target relocation frequency In the first cascaded rotational frequency shift, the value is taken as... In the second cascaded rotational frequency shift, the value is taken as Cascaded rotational frequency shifting is implemented recursively: after the first stage of frequency shifting, the signal frequency range changes from ( ) Expand to ( The sampling rate is from Upgraded to After the second-level frequency shift, the frequency range is from ( ) Expand to ( The sampling rate is from Upgraded to .

[0148] In one or more embodiments, when the system is implemented as an FPGA or ASIC chip, a global clock distribution network and pipeline synchronization registers are set up internally to ensure data consistency and timing correctness in multi-channel parallel processing. Data transfer between modules is achieved through AXI-Stream or a similar high-speed serial data interface protocol, ensuring strict sample-level synchronization when the four parallel data streams enter the time-domain overlay and reconstruction module.

[0149] In one or more embodiments, the system further includes an error detection unit connected to the outputs of each stage of the multi-stage interpolation and half-band filtering upsampling module, configured to detect the power and spectral purity of each branch signal. In response to detecting that the image rejection ratio of a branch is lower than a preset threshold, the error detection unit triggers the half-band filtering submodule of that branch to perform filter coefficient reloading or order boosting operations.

[0150] In one or more embodiments, the system achieves protection subcarrier elimination at the OFDM system level through the coordinated operation of the above four modules, with a spectrum utilization rate of 100%. Moreover, the multiplier resource consumption of the half-band filter submodule is reduced by more than 50% compared with the high-order anti-aliasing filter in the standard OFDM modulator, which significantly saves chip area and power consumption.

[0151] refer to Figure 10 This diagram illustrates a wireless communication transmitting apparatus according to one or more embodiments of this application. The transmitting apparatus includes a baseband signal processing unit, an OFDM modulator (i.e., the aforementioned system), a digital-to-analog converter, an RF up-conversion module, a power amplifier, and an antenna. The apparatus can be implemented as any one of a 4G LTE base station, a 5G NR base station, a 6G base station, a user terminal device, a WiFi access point, or a mobile communication relay node.

[0152] In one or more embodiments, the baseband signal processing unit is configured to generate a modulation symbol sequence to be transmitted. Specifically, the unit includes a channel coding submodule, an interleaving submodule, and a symbol mapping submodule. The channel coding submodule performs Turbo coding, LDPC coding, or Polar coding on the input service data bitstream to generate a coded bit sequence; the interleaving submodule performs interleaving processing on the coded bit sequence to combat burst errors; the symbol mapping submodule maps the interleaved bit sequence into a complex modulation symbol sequence according to modulation schemes such as QPSK, 16QAM, 64QAM, or 256QAM, and maps the symbol sequence to the corresponding subcarrier positions according to the resource block allocation scheme.

[0153] In one or more embodiments, the OFDM modulator (i.e., the aforementioned unprotected subcarrier OFDM modulation system based on four-way split IFFT end-shift frequency shift) is connected to the baseband signal processing unit and configured to modulate the modulation symbol sequence into an OFDM time-domain waveform with unprotected subcarriers. The OFDM modulator includes a subcarrier splitting and narrowband IFFT modulation module, a multi-stage interpolation and half-band filtering upsampling module, an end-complex exponential frequency shift module, and a time-domain superposition and reconstruction module.

[0154] Specifically, the subcarrier splitting and narrowband IFFT modulation module receives the modulation symbol sequence from the baseband signal processing unit, and evenly splits all effective subcarriers into four groups according to the four quadrants of the digital frequency circle. Each group undergoes an N / 2-point IFFT (activating only the middle N / 4 frequency points), generating four narrowband OFDM sub-band signals near the zero frequency. The multi-stage interpolation and half-band filtering upsampling module independently performs two stages of "2x interpolation + half-band filtering + rotation mixing" and two stages of "2x interpolation + half-band filtering" operations on the four signals. The final complex exponential frequency shift module applies a modulating frequency to each channel at the final sampling rate. The rotation factor completes the spectrum shift. The time-domain superposition and reconstruction module superimposes the four signals and outputs a complete OFDM time-domain waveform.

[0155] In one or more embodiments, the digital-to-analog converter (DAC) is connected to the OFDM modulator and configured to convert the OFDM time-domain waveform from the digital domain to an analog baseband signal. The DAC's sampling rate matches the output sampling rate of the OFDM modulator, and its resolution is not less than 14 bits to ensure the dynamic range of the output signal.

[0156] In one or more embodiments, the RF upconversion module is connected to the digital-to-analog converter and configured to upconvert the analog baseband signal to an RF carrier frequency. Specifically, the module includes a local oscillator and a mixer. The local oscillator generates a sinusoidal signal at the target RF carrier frequency, and the mixer mixes the analog baseband signal with the carrier signal to generate an RF modulated signal.

[0157] In one or more embodiments, the power amplifier is connected to the RF upconversion module and configured to amplify the RF signal to the target transmit power level. The power amplifier operates in a frequency band covering the operating frequency band of the device (e.g., 700MHz to 3.5GHz or millimeter-wave band), and its linearity meets the system EVM and ACLR requirements.

[0158] In one or more embodiments, the antenna is connected to the power amplifier and configured to radiate radio frequency signals into free space. The antenna may be a single antenna element or a multi-antenna array, supporting MIMO beamforming.

[0159] In one or more embodiments, the wireless communication transmitter further includes a cyclic prefix insertion module disposed between the OFDM modulator and the digital-to-analog converter, configured to insert a cyclic prefix at the leading end of the OFDM time-domain waveform to combat multipath fading. In this architecture, the insertion of the cyclic prefix occurs after time-domain superposition and reconstruction, and its parameters (CP length) are consistent with those of a standard OFDM system, ensuring compatibility with existing receivers.

[0160] In one or more embodiments, the four subcarrier subsets in the OFDM modulator can be independently configured with different modulation orders. For example, in a fragmented spectrum utilization scenario, the first sub-band (corresponding to the low-frequency band) uses 64QAM high-order modulation, and the fourth sub-band (corresponding to the high-frequency band) uses QPSK low-order modulation to adapt to the poor channel conditions in the high-frequency band.

[0161] In one or more embodiments, the resource block mapping in the baseband signal processing unit is specifically implemented as follows: Based on the resource allocation indication of the system scheduling, the set of effective subcarriers allocated to the user within the current transmission time interval is determined; the subcarrier set is then divided into frequency ranges (…). ), ( ), ( )and( The modulation symbol sequence is divided into four groups; the corresponding modulation symbol sequence is sent to the four parallel IFFT branches of the OFDM modulator.

[0162] In one or more embodiments, to ensure the security of the transmitting device during transmit / receive switching in TDD (Time Division Duplex) mode, the device further includes a transmit / receive switch control unit connected to the power amplifier and the antenna. This transmit / receive switch control unit connects the antenna to the output of the power amplifier during the transmit time slot, connects the antenna to the input of the receive link during the receive time slot, and inserts a guard interval during the switching gap to prevent the power amplifier from operating under antenna reflection mismatch conditions.

[0163] In one or more embodiments, in response to the power amplifier's output VSWR exceeding a preset threshold or the digital-to-analog converter's input signal amplitude exceeding full scale, the device performs an error handling procedure, including at least one of the following operations: reducing the output digital gain of the baseband signal processing unit, triggering a protective back-off of the power amplifier, recording an error log, and reporting it to a higher-level protocol stack of the baseband processing unit.

[0164] In one or more embodiments, the device, through the coordinated operation of the above-mentioned units and modules, achieves the generation of alias-free and low-spurious OFDM transmit waveforms without frequency domain protection subcarriers, while being fully compatible with the existing OFDM communication system. This effectively improves spectrum utilization and reduces baseband processing hardware overhead.

[0165] This application also provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, it can implement the steps of the method described in any of the preceding claims of this application. (Reference) Figure 1 The flowchart shown indicates that the computer program contains a sequence of program instructions corresponding to steps S1 to S4.

[0166] In one or more embodiments, when the computer program in the computer-readable storage medium is executed by a processor, it specifically implements the following functions:

[0167] Program instruction segment S1 is configured to: uniformly divide all effective subcarriers of the OFDM system into four subcarrier subsets according to the four quadrants of the digital frequency circle, corresponding to frequency intervals ( ), ( ), ( )and( Narrowband IFFT modulation is performed on each of the four subcarrier subsets, where N / 2-point IFFT transformation is used and only the N / 4 frequency points located in the middle carry the effective signal, generating four narrowband OFDM sub-band signals near the zero frequency. The effective bandwidth of each sub-band signal is constrained by ( Within the range.

[0168] The program instruction segment S2 is configured to: independently perform multi-level upsampling processing on the four narrowband OFDM subband signals. Each upsampling process includes performing a 2x interpolation operation on the subband signal at the current sampling rate, and then filtering the interpolated signal through a half-band filter to remove the mirror spectrum. No spectrum shifting operation is performed throughout the multi-level upsampling process.

[0169] Program instruction segment S3 is configured to: after all four narrowband OFDM subband signals have reached the system's final output sampling rate, apply a time-domain complex exponential rotation factor to each signal. Spectrum shifting is performed to move each signal from near zero frequency to its corresponding target quadrant frequency position.

[0170] The program instruction segment S4 is configured to superimpose the four sub-band signals that have completed spectrum shifting in the time domain to reconstruct a complete OFDM time-domain waveform without guarded subcarriers.

[0171] In one or more embodiments, when the computer program on the computer-readable storage medium is executed by a processor, it can also perform the following functions: each of the four sub-band signals can be independently turned on or off; when the frequency band corresponding to a certain channel is idle or unavailable, the modulation branch program segment of that channel is skipped to save computational power consumption.

[0172] In one or more embodiments, the cascaded rotation frequency shift implemented by the computer program on the storage medium is executed according to the following recursive relationship: the first execution of the "2x interpolation + half-band filtering + rotation mixing" operation adds the two branch signals and occupies the frequency spectrum range ( The sampling rate is from Upgraded to The second operation, "2x interpolation + half-band filtering + rotating mixer," sums the four branch signals to occupy the frequency spectrum range. The sampling rate is from Upgraded to Subsequently, two "2x interpolation + half-band filtering" operations are performed without frequency shifting, reducing the sampling rate from... Upgraded to .

[0173] In one or more embodiments, when the computer program on the computer-readable storage medium is executed by a processor, in a multi-threaded or parallel processing environment, a semaphore mechanism is used to ensure mutual exclusion of each program instruction segment's access to the IFFT coefficient table and filter coefficient table in shared memory.

[0174] In one or more embodiments, when the computer program on the computer-readable storage medium is executed by a processor, it also implements an error handling process: in response to an abnormal interpolation filter output signal power of any sub-band branch, it performs at least one of the following operations: terminating subsequent processing of the branch, logging an abnormal event, and reloading the filter coefficients.

[0175] In one or more embodiments, the computer-readable storage medium may include, but is not limited to, read-only memory (ROM), random access memory (RAM), magnetic disk, or optical disk. By executing a computer program on the storage medium, the OFDM modulation method of this application can be implemented on a general-purpose processor or digital signal processor, facilitating the deployment of the technical solution of this application on existing communication equipment through software upgrades.

[0176] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, the phrase "comprising an element defined as..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0177] The above technical solutions only embody the preferred technical solutions of the present invention. Any modifications that may be made by those skilled in the art to certain parts therein embody the principles of the present invention and fall within the protection scope of the present invention.

Claims

1. A method for unprotected subcarrier OFDM modulation based on four-way split IFFT end frequency shift, characterized in that, The method does not set any frequency domain protection subcarriers, and all N subcarriers are effective data subcarriers, achieving 100% spectrum utilization. The method includes the following steps: Step S1: Divide all effective subcarriers of the OFDM system into a first subcarrier subset, a second subcarrier subset, a third subcarrier subset, and a fourth subcarrier subset according to the four quadrants of the digital frequency circle; Wherein, the first subcarrier subset corresponds to the frequency range ( The second subcarrier subset corresponds to the frequency range ( The third subcarrier subset corresponds to the frequency range ( The fourth subcarrier subset corresponds to the frequency range ( ), This refers to the system baseband sampling rate; Narrowband IFFT modulation is performed on the first, second, third, and fourth subcarrier subsets respectively to generate four narrowband OFDM subband signals near the zero frequency. The effective bandwidth of each subband signal is constrained by ( Within the range; The narrowband IFFT modulation in step S1 is implemented as follows: an N / 2-point IFFT transform is used, where only N / 4 frequency points located in the middle of the transform domain carry effective signals, and the remaining frequency points are set to zero, so that each sub-band signal forms a bandwidth of ( ) near the zero frequency. Narrowband signal; Step S2: Perform multi-level upsampling processing independently on the four narrowband OFDM subband signals. Each upsampling process includes: A 2x interpolation operation is performed on the subband signal at the current sampling rate, and then the interpolated signal is filtered by a half-band filter to remove the mirror spectrum. The entire process of the multi-level upsampling process does not involve spectrum shifting. Step S3: After all four narrowband OFDM sub-band signals have reached the final output sampling rate of the system, apply a time-domain complex exponential rotation factor to each narrowband OFDM sub-band signal to perform spectrum shifting, and shift each narrowband OFDM sub-band signal from the vicinity of zero frequency to its corresponding target quadrant frequency position. The expression for the time-domain complex exponential twitch factor in step S3 is: ,in The time-domain sample number, The imaginary unit is used to achieve a positive frequency shift when the rotation factor is positive. Frequency reversal is achieved when the rotation factor is negative. ; Step S4: Superimpose the four narrowband OFDM subband signals that have completed spectrum shifting in the time domain to reconstruct a complete OFDM time-domain waveform without guarded subcarriers.

2. The method according to claim 1, characterized in that, The multi-stage upsampling process in step S2 includes a combination of two-stage rotation-frequency shift operations and two-stage pure upsampling operations, specifically: The first execution of the "2x interpolation + half-band filtering + rotating mixer" operation adds the two branch signals together, occupying the corresponding frequency range. The sampling rate is from Upgraded to ; The second execution of the "2x interpolation + half-band filtering + rotating mixer" operation sums the four branch signals, occupying the corresponding frequency range. The sampling rate is from Upgraded to ; Subsequently, two "2x interpolation + half-band filtering" operations are performed without frequency shifting, reducing the sampling rate from... Upgraded to .

3. The method according to claim 1, characterized in that, The frequency mapping relationship of the subcarrier subsets of the four paths satisfies the following conditions: After the first rotational mixing or Then, the first signal comes from ( , Mapped to ( The second signal comes from ( Mapped to ( The third signal comes from ( Mapped to ( The fourth signal comes from ( Mapped to ( ); After a second rotational mixing process or Then, the first signal is finally mapped to ( The second signal is ultimately mapped to ( The third signal is ultimately mapped to ( The fourth signal is ultimately mapped to ( ).

4. The method according to claim 1, characterized in that, Each of the four narrowband OFDM sub-band signals can be independently turned on or off. When the frequency band corresponding to a narrowband OFDM sub-band signal is idle or unavailable, the modulation branch of that narrowband OFDM sub-band signal is turned off to save computational power consumption.

5. A four-way split IFFT end-frequency shifting unprotected subcarrier OFDM modulation system, the system being used to implement the method as described in any one of claims 1 to 4, characterized in that, include: The subcarrier splitting and narrowband IFFT modulation module is configured to evenly split all effective subcarriers of the OFDM system into four subcarrier subsets according to the four quadrants of the digital frequency circle, and independently perform narrowband IFFT modulation on each subcarrier subset to generate four narrowband OFDM subband signals near the zero frequency. The multi-level interpolation and half-band filtering upsampling module is connected to the subcarrier splitting and narrowband IFFT modulation module and is configured to independently perform multi-level "2x interpolation + half-band filtering" upsampling processing on the four narrowband OFDM subband signals, without performing spectrum shifting throughout the process. The end complex exponential frequency shifting module is connected to the multi-level interpolation and half-band filtering upsampling module. It is configured to apply a complex exponential rotation factor to each narrowband OFDM sub-band signal to shift it to its respective target quadrant frequency position after the four narrowband OFDM sub-band signals reach the final output sampling rate of the system. The time-domain superposition and reconstruction module is connected to the end complex exponential frequency shifting module and is configured to superimpose the four frequency-shifted narrowband OFDM subband signals in the time domain to generate a complete OFDM time-domain waveform without guarded subcarriers.

6. A wireless communication transmitting device, characterized in that, include: The baseband signal processing unit is configured to generate a sequence of modulation symbols to be transmitted; The system as described in claim 5, connected to the baseband signal processing unit, is configured to modulate the modulation symbol sequence into an OFDM time-domain waveform with unguarded subcarriers; A digital-to-analog converter, connected to the OFDM modulator, is configured to convert the OFDM time-domain waveform into an analog baseband signal; An RF upconversion module, connected to the digital-to-analog converter, is configured to upconvert the analog baseband signal to the RF carrier frequency; A power amplifier, connected to the radio frequency upconversion module, is configured to amplify the power of the radio frequency signal; An antenna, connected to the power amplifier, is configured to radiate radio frequency signals into free space.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it is able to implement the steps of the method as described in any one of claims 1 to 4.

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